Wind turbines are devices that convert mechanical energy to electrical energy. A typical wind turbine includes a nacelle mounted on a tower housing a drive train for transmitting the rotation of a rotor to an electric generator and other components such as a yaw drive which rotates the wind turbine, several controllers and a brake. The rotor supports a number of blades extending radially therefrom for capturing the kinetic energy of the wind and causing the driving train rotational motion. The rotor blades have an aerodynamic shape such that when a wind blows across the surface of the blade, a lift force is generated causing the rotation of a shaft which is connected—directly or through a gearing arrangement—to the electrical generator located inside the nacelle. The amount of energy produced by wind turbines is dependent on the rotor blade sweeping surface that receives the action from the wind and consequently increasing the length of the blades leads normally to an increase of the power output of the wind turbine.
Under known control methods and systems the power produced by a wind turbine increases with wind speed until a rated nominal power output is reached and then it is maintained constant. This is done regulating the pitching action of the blades so that the rotor blade's pitch angle is changed to a smaller angle of attack in order to reduce power capture and to a greater angle of attack to increase the power capture. Therefore the generator speed, and consequently, the power output may be maintained relatively constant with increasing wind velocities.
However in case of gusts and turbulences wind speed may change drastically in a relatively small interval of time requiring relatively rapid changes of the pitch angle of the blades to maintain constant the power output that are difficult to implement taking into account the dynamics of the pitch control actuator and the inertia of the mechanical components. As a result, generator speed may exceed the over speed limit and the wind turbine is shut down to avoid damages.
The power and rotor speed regulation implemented in most of the known commercial wind turbine control systems is based on a Proportional-Integral-Derivative (PID) approach which reacts to already produced errors between measured variables and its set points with its associated limitations.
In order to solve this problem there are known several proposals of control systems improving its performance particularly under wind speed varying conditions such as the proposal disclosed in WO 2008/046942 A1.
On the other hand there are known many general-purpose control systems. One of them is the adaptive predictive control system disclosed in Spanish Patents 460649 and 2206315 but the applicant does not know any proposal of an adaptive predictive control system for wind turbines.
Adaptive predictive controllers drive the controlled variable to desired values (set points) reacting to non-already produced errors. These controllers are based on an internal plant model in order to predict its future states. A second functionality is introduced when adapting the internal plant dynamic model parameters in order to take into account the plant evolutions. This kind of controllers require information in execution time which differs from the one used by the PID controllers. Consequently the use of these controllers in particular areas can not be carried out without deep strategy studies.
Therefore the known proposals involve the use of more information (particularly statistical data) than in commercial control systems and/or improved tools for the analysis of the relevant information but none of them provide a clear control strategy, easy to implement, that can cope with situations of rapid changes of the wind speed.
This invention is intended to solve this drawback.